Effect of initial ziprasidone dose on treatment persistence in schizophrenia C. Daniel Mullins a, * , Fadia T. Shaya a , Julie Magno Zito a , Nour Obeidat a , John Naradzay a , David J. Harrison b a University of Maryland School of Pharmacy, 515 W. Lombard Street, Room 262, Baltimore, MD 21201, United States b Pfizer Inc., U.S. Outcomes Research Department, 235 E 42nd Street, New York, NY 10017, United States Received 20 October 2005; received in revised form 13 January 2006; accepted 18 January 2006 Available online 20 March 2006 Abstract Objective: To determine the relationship between ziprasidone initial dose and treatment persistence among patients diagnosed with schizophrenia. Method: Adult Medicaid recipients (N = 1096) diagnosed with schizophrenia who had ziprasidone prescription claims between July 1, 2001 and September 30, 2003, were categorized by initial dose: low (20–60 mg per day, n = 464), medium (61–119 mg per day, n =320) and high dose (120–160 mg per day, n =312). Treatment persistence up to 365 days was measured using refill patterns, allowing 15-day gaps between expected refill dates. Multivariate survival analysis explored the simultaneous impact of age, gender, race, previous hospitalization, and concomitant medication usage, in addition to initial dose of ziprasidone. Sensitivity analysis tested the robustness of results with different definitions for persistence and allowable gaps between refills. Results: Discontinuation rates across the observation period (maximum, 12 months per individual) were lower for patients initiated with high-dose than low-dose ziprasidone ( P = 0.001). Other factors significantly associated with greater discontinuation of medication were monotherapy (versus combination therapy) and hospitalization within the 6 months prior to the index date of therapy. Black race was associated with greater discontinuation, although this was not consistent across sensitivity analyses. Conclusions: Patients with schizophrenia started on high doses of ziprasidone have lower discontinuation rates in a retrospective Medicaid database than patients started on low doses. These results were robust across various sensitivity analyses. D 2006 Elsevier B.V. All rights reserved. Keywords: Persistence; Schizophrenia; Ziprasidone; Medicaid; Atypical antipsychotic 1. Introduction Successful management of schizophrenia is depen- dent on patient adherence to recommendations for consistent and long-term antipsychotic therapy (Keith and Kane, 2003). Adherence to therapy can substan- 0920-9964/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.schres.2006.01.013 * Corresponding author. Tel.: +1 410 706 0879; fax: +1 410 706 5394. E-mail address: dmullins@rx.umaryland.edu (C.D. Mullins). Schizophrenia Research 83 (2006) 277 – 284 www.elsevier.com/locate/schres